US President Joe Biden has warned all sides involved in the negotiations for a possible Gaza ceasefire deal not to undermine efforts.

Biden declared that “we are closer than we’ve ever been” to a ceasefire following the latest round of negotiations, but a senior Hamas official expressed scepticism.

The president also announced he was sending Secretary of State Antony Blinken to Israel to continue the “intensive efforts to conclude this agreement”.

His comments come following a joint statement by the US, Qatar and Egypt – stating that they had presented a proposal for a ceasefire and hostage release deal that “narrows the gaps” between Israel and Hamas.

Any sign of progress in the Qatar talks is regarded as essential by governments desperate to avoid the war in Gaza spiralling into an all-out regional conflict.

The mediators said that the past two days of ceasefire discussions had been “serious, constructive and conducted in a positive atmosphere”.

Technical teams are expected to continue working over the coming days on the details of how to implement the proposed terms before senior government officials meet again in Cairo, hoping to reach an agreement on the terms set out in Doha.

Mr Biden later said in a statement that he had spoken separately with the leaders of Qatar and Egypt, who had expressed “strong support” for the proposal.

He added that he was also sending Mr Blinken back to the Middle East to “reaffirm my iron-clad support for Israel’s security” and to “underscore that with the comprehensive ceasefire and hostage release deal now in sight, no one in the region should take actions to undermine this process”.

While the mediators’ statement is clearly a positive development, there is still a long way to go before a ceasefire is agreed.

Nevertheless, Mr Blinken told US reporters that he had become more optimistic than ever that a deal was in reach but said if he revealed why, he’d “give it away”.

Asked when a potential ceasefire might start, he said “that remains to be seen”.

This is not the first time the US president has said he thought a deal was close and not everyone shares his cautious optimism.

A senior figure from Hamas – which did not participate in the talks, but was in contact with Qatari and Egyptian officials – told the BBC: “What the movement’s leadership was informed of today regarding the results of the Doha ceasefire meetings does not include a commitment to implement what was agreed upon on 2 July.”

Israeli Prime Minister Benjamin Netanyahu’s office, meanwhile, said he appreciated the efforts to “dissuade Hamas from its refusal on a deal that would release the hostages”.

The Israeli military launched a campaign in Gaza to destroy Hamas in response to an unprecedented attack on southern Israel on 7 October, during which about 1,200 people were killed and 251 others were taken hostage.

More than 40,000 people have been killed in Gaza since then, according to the territory’s Hamas-run health ministry.

A deal agreed in November saw Hamas release 105 of the hostages in return for a week-long ceasefire and the freeing of some 240 Palestinian prisoners in Israeli jails. Israel says 111 hostages are still being held, 39 of whom are presumed dead.

The first phase of the deal outlined by President Biden, based on Israel’s 27 May proposal, would include a “full and complete ceasefire” lasting six weeks, the withdrawal of Israeli forces from all populated areas of Gaza, and the exchange of some of the hostages – including women, the elderly and the sick or wounded – for Palestinian prisoners held in Israel.

The second phase would involve the release of all other living hostages and a “permanent end to hostilities”. The third would see the start of a major reconstruction plan for Gaza and the return of dead hostages’ remains.

Meanwhile, Israel’s military operation in Gaza continues, with new evacuation orders being made for several blocks in northern Khan Younis and Deir Balah – further shrinking the humanitarian zone.

Israel said the blocks had become dangerous for civilians “due to significant acts of terrorism” and the firing of rockets and mortars towards Israel.

The UN agency for Palestinian refugees (Unrwa) said: “Once again, fear spreads as families have nowhere to go. People remain trapped in an endless nightmare of death and destruction on a staggering scale.”

What is now making the need for a ceasefire deal even more urgent is the fact that the polio virus – which is spread through faecal matter – is now circulating inside the Israeli-designated humanitarian zone in Gaza, where hundreds of thousands of displaced Palestinians have sought refuge from the fighting.

“Let’s be clear: The ultimate vaccine for polio is peace and an immediate humanitarian ceasefire,” UN Secretary General António Guterres said.